Urbanization is a major driver of global species loss. While cities with suitable habitats and conservation policies may support locally-high biodiversity levels, we suspected that the complexity of managing very large cities might counteract the advantage of large geographic area, and these cities may be less effective at biodiversity conservation. To answer this, we examined the relationship between the number of native indicator wildlife species (mean and maximum) in 112 cities across three metropolitan areas in California (Los Angeles, San Diego, and San Jose), with metrics related to scale and environmental variables. We found that indicator species richness is positively related to area, income (the luxury effect), and pervious cover—including trees, shrubs, and grasses. Despite having a high maximum number of indicator species within their boundaries, the largest cities in our study, Los Angeles, San Jose, and San Diego, do a relatively poor job compared with smaller cities at distributing native biodiversity throughout neighborhoods, as measured by their mean species richness. Such variation in “neighborhood biodiversity” may exacerbate existing inequities in residents' access to nature. Using Los Angeles County as a case study, we compared biodiversity management within the County's 88 cities of various sizes and characteristics. We ranked General Plan wording in terms of references to biodiversity and conservation and created a management metric. We found that municipalities of various sizes that had high management scores generally had high indicator species richness. This suggests that robust policies may be able to overcome the challenges posed by city size and population.

Spanning more than 73 km across two counties at the western border of the Los Angeles metropolitan area, the Santa Monica Mountains represent both a major landform as well as a unique urban-adjacent open space for millions of residents throughout southern California. Critically, they are essential for the maintenance of high levels of biodiversity within a global biodiversity hotspot that includes a major metropolis. The Los Angeles County portion of the Santa Monica Mountains (LASMM), spanning approximately 62 km from the Los Angeles River at the eastern edge of Griffith Park to the Los Angeles – Ventura County Line, contains substantial public open space, protected from encroaching development in the growing metropolis. In order to understand how these protected areas were established, we gathered information regarding over 3,000 parcels of public open space and their acquisition dates and owners, and examined the history of land conservation in the LASMM to determine the roles and relationships of key stakeholders. These stakeholders have included residents, activists, scientists, legislators, non-governmental organizations (NGOs), and land management agencies. We suggest that there is a virtuous cycle, or positive feedback loop over time, as open space protection is informed by, and influences, advocacy, land use policies, and habitat conservation. This interplay of stakeholders has been refined over several decades, and may offer lessons for other regions working to produce similar results in durable open space conservation.